This invention relates to decorative sheet-type covering material and especially to a method for preparing suitable substrate for such material.
Decorative, flexible sheet-type covering materials such as wall or floor coverings are well-known. Frequently, such coverings involve the use of a chemically blown foamable plastic applied in a liquid state to a substrate. The foamable liquid is then gelled, frequently printed with a design, and expanded by heat to e.g. three times its original thickness. Conventional use of such chemically foamed material is described for instance in U.S. Pat. No. 3,458,337 and U.S. Pat. No. 3,293,094, the disclosures of which are incorporated herein by reference.
While the use of chemically foamed plastic over substrates in the production of sheet covering materials is well-known and has been extensively practiced, the resulting products have not always been entirely satisfactory. Where porous substrates or irregular substrates have been used, results have been less than satisfactory since irregularities in substrate or penetration of the foamable liquid coating into the supporting substrate results in magnified surface distortions in the finished product. This is especially noticeable where printed patterns are formed on the foamed layer or are printed onto an unfoamed layer prior to foaming of the layer.
The use of non-foamable material for sealing and coating a porous or irregular substrate has been generally unsatisfactory due to penetration of the coating material into the openings in the porous substrate.
In addition to chemically foamed plastics of the type mentioned above, mechanically foamed plastics in which air or other gas is introduced into the plastic as by beating or other forms of mechanical aeration are well known, as exemplified for instance in U.S. Pat. No. 3,511,788, the disclosure of which is also incorporated herein by reference. Such mechanically foamed plastics have been suggested for a variety of purposes such as in very thin layers for application to a variety of substrates as suggested in the above-mentioned U.S. Pat. No. 3,511,788. Such foams have also been utilized as backing for sheet covering materials, especially flooring to provide resiliency under foot.
It is also quite common in the flooring industry to make an embossed foam product either by use of chemical means such as suppresent inks, etc., in the manner taught by the above-mentioned U.S. patents or by mechanical embossing of the foamed layer or completed product. Mechanical embossing is a well known technique as exemplified for instance by the more detailed descriptions in U.S. Pat. Nos. 3,345,234, 3,748,151 and 3,887,678.